Enhanced Supercapacitive Performance of MnCO3@rGO in an Electrolyte with KI as Additive

MnCO3@rGO (GM) was synthesized through a facile one-pot hydrothermal process with graphene oxide and KMnO4 as precursors. X-ray diffraction analysis reveals that the prepared MnCO3 possesses a high crystallinity with a grain size of 28.4 nm. To improve the capacitive performance of GM, KI was added to the Na2SO4 electrolyte as a redox additive. Electrochemical measurements show that the specific capacitance of GM in KI additive electrolyte could reach up to 546 F g(-1) at the current density of 0.5 A g(-1). This value is 8 times larger than that (61 F g(-1)) in Na2SO4 electrolyte at the same current density. The elevated specific capacitance is attributed to the presence of I-, which can bring about significant pseudocapacitance through the redox couples of I-/I-3(-) and I-/IO3- as confirmed by X-ray photoelectron spectroscopy. GM also possesses a capacitance retention ratio of around 103 % after 2000 cyclic voltammetry measurements, suggesting a superior cycling stability.